The use of contact lenses to correct vision is common place in today's world. There are presently several traditional methods of high-volume low-cost contact lens manufacture. These methods include, but are not limited, to cast molding, spin casting, lathing, and using a technique known in the industry as “Lightstream Technology”, and any combinations thereof.
Traditional cast molding involves the use of diamond point turning technologies to produce metal tools (also referred to as inserts) that are used in the injection molding process to produce male and female plastic lens molds. Liquid monomer is placed between the pair of male/female molds and is cured. Subsequently, the cured lens is removed from the mold pair and undergoes post processing steps (including hydration, release, sterilization, inspection, measurement, packaging, etc.) which results in a usable product.
Typically, spin casting also involves the use of diamond point turning technologies to produce metal tools that are used in the injection molding process to produce female plastic lens molds, into which liquid monomer is dosed. The mold and monomer are then spun about a central axis while being exposed to curing radiation and the lens is formed. Similar to cast molding, the cured lens is removed from the lens mold and undergoes post processing steps (including hydration, release, sterilization, inspection, measurement, packaging, etc.) which results in a usable product.
Typically, lathing involves the use of diamond point turning technologies to produce pre-hydrated lenses directly from lens blanks (also called buttons). The pre-hydrated lens then undergoes post processing steps including hydration, sterilization, inspection, measurement, packaging, etc., which results in a usable product.
Diamond point turning can also be used to produce the lens molds directly, with these lens molds being utilized in the cast molding or spin casting descriptions above.
“Lightstream Technology” is a technology used by Ciba Vision Corporation of Duluth, Ga. (now Alcon) which involves the use of re-usable glass mold pairs instead of plastic molds. Each glass mold pair consists of a concave surface mold and a convex surface mold that are submerged in lens monomer, placed close to each other so that the gap between the two curved surfaces map to the desired pre-hydrated contact lens profile. The monomer is cured through the glass molds using ultraviolet light, the molds separated and then the lens undergoes stages including hydration, sterilization, inspection, measurement, packaging, etc., which results in a usable product.
Most contact lenses produced and sold today are in discrete parameter ranges, which include limited base curves, diameters and powers. Sphere power offerings vary by manufacturer, but are usually in the range of −20.00 D to +20.00 D, more likely −12.00 D to +8.00 D. Typically, powers within these ranges are only offered in 0.25 D steps (between the range of −6.00 D and +6.00 D powers) and 0.50 D steps outside the ±6.00 D range. Currently, most cylinder power offerings are also in discrete steps, with each manufacturer having their own ranges. The Acuvue® brand of astigmatic lenses, manufactured and sold by Johnson & Johnson Vision Care of Jacksonville, Fla., for example, currently only offers −0.75 D, −1.25 D, −1.75 D and −2.25 D of cylinder correction. The available power axes of astigmatic lenses are also limited, typically in 10° steps, ranging from 0° to 180° for low cylinder powers, and restricted by some manufacturers further to say 80°, 90°, 100°, 170°, 180° and 190° (the 180° and 190° angles may be referred to as the 0° and 10° angles respectively) offerings for high cylinder powers.
The reasons for manufacturers only offering discrete steps in contact lens parameters are many, but may include the cost of tool and mold manufacture, inventory costs for storing large numbers of stock keeping units (SKUs) of the tools, inventory costs of storing huge quantities of lenses, the low prevalence of patients needing higher degrees of power correction, etc. As an example, consider the number of SKUs for a fictional astigmatic product called “BrandX” which has 1 base curve offering and 1 diameter offering. A sphere power range of −6.00 D to +6.00 D in 0.25 D steps for BrandX results in 49 different SKUs. Cylinder power offerings of say −0.75 D, −1.25 D, −1.75 D and −2.25 D along just one axis quadruples the number of SKUs to 196. Axis offerings for BrandX, say at every 10° for each of the cylinder powers, multiplies the SKUs by 18 to give 3528 SKUs. Each incremental cylinder power offering at each of the 10° axes adds 882 SKUs to BrandX's portfolio. If cylinder powers were offered in 0.25 D steps from −0.25 D to −2.25 D, the total number of BrandX SKUs would be 7938. Just one additional base curve offering doubles the SKUs to 15,876, and adding just one other diameter to the mix doubles the total again to 31,752 SKUs. Offering BrandX's axes in 5° instead of 10° increments also doubles the number of SKUs to 63,504. Offering BrandX in alternate materials also drastically increases the number of SKUs.
Offerings of different lens designs, power, base curve, diameter and shape all require different tools to be made. In a cost range of $100-$500 per metal tool, cast molding for a large number of SKUs is a very expensive proposition, especially when multi-cavity technology is used wherein multiple tools of the same design are used in each mold block. Manufacturers therefore are selective as to the number of different contact lens design options they produce, which typically are chosen to align with the most commonly prevalent vision need/ordered prescriptions. This, of course, means that individuals whose prescriptions fall between or outside those ranges offered by manufacturers must purchase lenses that are less than optimal in correcting their particular vision or fit needs.
More recently, a new system and method for manufacturing contact lenses has been disclosed in which an infinite number of different lens shapes and lens parameters (including lens powers) can be produced on a custom basis. U.S. Pat. No. 8,317,505, which is incorporated herein by reference in its entirety, discloses a method for growing a Lens Precursor Form on a single male optical mandrel on a voxel by voxel basis by selectively projecting actinic radiation through the optic mandrel and into a vat or bath of liquid polymer. The optical mandrel and Lens Precursor Form are then removed from the vat and inverted so that the convex surface of the optic mandrel is upright. Following a dwell period during which uncured residual liquid monomer from the bath that remains on the Lens Precursor Form flows under gravity over the Lens Precursor Form, such liquid is then cured to form the final lens. As described therein, a custom lens can be produced for any given eye.
The ability to manufacture highly precise and truly custom contact lenses will be truly beneficial to a patient only so far as a truly accurate, custom prescription can be generated for that patient.
The conventional method for performing an initial determination of the corrective needs for a patient leverages the well-known phoropter devices, which depend on subjective input from the patient to advise the eye care practitioner as to which of various lenses placed before his or her eye provides better corrected vision. Phoropters, however, typically have discrete, stepped resolutions for focus error and cylindrical error, usually 0.125 and 0.25 diopters respectively, although some newer devices can achieve higher resolutions of 0.01 diopters. Zeroing in on an accurate corrective need for a patient using a phoropter is a time consuming process, with at each step the practitioner having to use judgment to select the next proposed lens and manually do so, and the patient having to compare one selection to the other and provide feedback to the practitioner. With three independent variables, focus error, cylindrical power and cylindrical axis, time constraints may limit the accuracy of the end result. Human error, both that of the patient and the practitioner, are necessarily present. Further, subjective determination of cylindrical axis is difficult because slight differences can have a large impact on cylindrical correction. Further, as indicated, the accuracy of a determined corrective need is limited by the resolution of the phoropter used. Phoropters can determine sphere, cylinder and axis, but not higher order aberrations.
Objective measurement devices and techniques have also been used to measure a patient's eye and subsequently determine corrective needs for that patient. These devices, known as refractometers and aberrometers, typically display sphere power data to the nearest one hundredth of a diopter, and the nearest whole integer for axis in degrees. Exams performed using refractometers and aberrometers are typically referred to as “objective exams” since the equipment returns numerical and graphical values with little to no patient involvement in the decision making process. One example of an auto-refractometer is the Nidek ARK-10000 Refractive Power/Corneal Analyzer (Nidek Inc. of Freemont, Calif.). The 0.01 D power resolution and 1° axis resolution of refractometers and aberrometers suggests that they would be ideal for use in the process of prescribing custom lenses. Objective exams, however, do not take into account how the brain perceives and analyzes the images presented to it by the ocular system and, therefore, do not always provide the best prescriptive data for all patients. When fitted with lenses prescribed via the use of subjective data compared to lenses prescribed based on objective data, some patients prefer the “subjective lenses” and others prefer the “objective lenses.” This being said, the sphere, cylinder and axis data from objective exams can be used alone, or in combination with data from subjective exams to provide the best possible custom lens design for the patient.
Some attempts have been made to combine subjective feedback obtained using a phoropter with objective data such as that obtained from an aberrometer. One such example is described in U.S. Patent Publication No. 2014/0368795. Although this method does describe leveraging a combination of objective and subjective data, it is still plagued by the disadvantages of the phoropter described above, most notably the time consuming process, involvement of the practitioner in the process, and patient difficulty in choosing at each steps which of two options is better when lenses are flipped back and forth before them.